Constant frequency oscillator



Feb. 7, 1933. LLEWELLYN 1,896,781

CONSTANT FREQUENCY OSCILLATOR Filed March 16, 1931 2 Sheets-Sheet l K I a ix,,,=z'a;x 65

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K L L C 2 i 5 -H-msm K MYVENTOR k5. LLEWELLYN T ATTORNEY Feb. 7, 1933. wE1 1,896,781

CONSTANT FREQUENCY OSCILLATOR 2 Sheds-Sheet 2 Filed March 16, 1951 FIG. 8

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I65 If INVENTOR E 8,. LLEWELL r/v TM AT TORNEV FREDERICK B. LLEWELLYN, OF MONTCLAIR, JERSEY, ASSIGNOR TO BELIi- TELE-- Patented Feb. 7, 1933 UNITED" STATES,

PATENT emee PHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION N EW YORK CONSTANT FREQUENCY OSCILLATOR Application filed March 16, 1931. Serial No. 522,941. 1

This invention relates to constant frequency electric discharge oscillators or,-more specifically, to simple modifications of existing conventional types of electric discharge oscillators whereby their frequency stability is increased without detriment to their normal functions.

' One object of the invention is to improve the frequency stability of conventional types of electric discharge oscillator circuits as af-' fected especially by changesin operating or battery voltages or in load resistance, these being the more common contributing causes of frequency variation. Another object of the invention is to evolve critical impedance relations in such conventional types of oscillators so as to achieve frequency stability as affected by changes in operating (for example, battery) voltages or of load resistance, or as affected jointlyby such types of variations. Y Y A A further object of the. invention is to achieve stabilization at frequencies at which inter-electrode .capacities of the space "discharge device employed in ,such oscillators produce an appreciableeffect.

Still another objectofthe invention is to achieve frequency stabilization with respect to the above mentioned changes with maximum simplicity of circuit, economy of plant and reliability of function; and especially with avoidance of dependence on the parameters of the space discharge device employed in the conventional feed-back oscillator. a

In my copending application, Serial No.

i 47 8,37 3, filed August 28,1980, several oscil lating systems are described inwhich frequency variations resulting from changes in battery voltages and load resistance are substantially eliminated by utilizing a critically valued reactance between-the frequency determining circuit and thegrid, or plate, or both. In the present invention frequency stabilization with respect to such changes is accomplished in magnetic feed-back oscillators by including a stabilizing reactance in the frequency determining circuit, the reactance being of such value that an effective unity coupling between the'input and output circuits of the tube employed is obtained. One important advantage resulting from stabilizing feed-back oscillators in accordance with this invention'is that the frequency of the oscillator may easily be stabilized at all frequencies, including relatively high frequencies at which the inter -electrode capaci ties of the space discharge device possessappreciable values.

Since the changes in operating (for example battery) voltages and load resistance are the principal factors inthe frequency change, an. oscillator whose frequency is stable so far as affected by such changesmay be regarded as a frequency stable oscillator for all practical purposes except as the reactive frequency determining elements may be affected by teniperature 'c'hanges. It happens in accoi dance with this invention that an oscillator Whose frequency is stable with respect to changes in voltages may,bythe use of means to be described, be" made stable with respect to load resistance.

Other advantages and aspects of the invention will'be apparent from the following description, when read in connection with the accompanying drawings in which:

Fig. 1 lllustrates a dlagrammatic circuit which is useful for mathematical analysis of i Y the circuits shown in the other figures;

Fig. 2 illustrates a generalized circuitja'rranged for input or grid stabilization;

Fig. 3 illustrates a feed-back oscillator with grid stabilization; I

f Fig. a is a-I-Iartley oscillatorarranged for grid stabilization; a

Fig. '5 illustrates a generalized circuit arranged. for output or plate stabilization;

Fig. 6 illustrates a reversed feed-back oscillator with plate stabilization;

Fig. 7 illustrates a Hartley oscillator with plate stabilization t I Fig. 8' illustrates a generalized circuit ar-' ranged for both grid and plate stabilization;

Fig. 9 illustrates a reversed feed-back oscillator arranged: for both grid and plate stabilization; l I

Fig. 10 illustrates a feed-back circuit v y mg both the grid and plate circuitsstabi-f e a ,@1o0f' lized Fig. 11 illustrates a Hartley oscillator with both grid and plate sta'loilized;.and Fig. 12 is'a wiring diagram of an oscillator having both grid and'plate stabilized in accordance with the invention. I

Referring to Fig. 1, the mathematical theory underlying the invention will be considered in detail, the designations listed becircult 1Z impedance associated with the input circuit; and

Z plate-grid impedance InFig 1 the two windings of the transformer with effective unity coupling are shown-by react'ances X and X From the properties of unity coupled coils, at either a low or high frequencies, we have Themsince 7 E r l Z (2) where Z is theimpedance as seen looking out of the plate side of the tube, we have, from,(1) and (2) 7 g it This equation completely expresses-the operation of the oscillator insofar as impedance relations for'the fundamental current component are concerned. 1 By ordinary circuit anaylsls, it may be showirthat Z is given by the following expression:

li L 213 X taxis; 1+ X1 (4) Substitution of this into gives the tube, 4 maybe separated into two parts,

the one z'X in parallel with the other which constitutes the grid resistance r Both Z and Z, are taken as pure reactances. Thus the last expression yields the two equations:

i i" i nyt Xi nXJ XI 211 (5) Equation contains neither r 1' nor so that we reach theimportant conclusion that the frequency of an oscillator with unity coupling between the plate and grid circuits depends only upon the inductances and capacities in the circuit, and not at all upon the tube parameters, r r and a; provided, however, that the losses in the ex-. ternal circuit are small, and. the harmonic voltages across the tube are small enough to allow 1 and r to be considered as pure resistances. In this connection itis, important to note that the interelectrode capacities C may be grouped with the :externalcircuit elements formingX X and X ,-so that no high frequency difficulty isto be anticipated from them.

Equation (6) contains the relationbetween TD, r and ,u. necessary to insure the presence of oscillation. In practice, the amplitude of the oscillations builds up until this relation is Y satisfied. I V v v The foregoingftheory of theaction of a unity coupled oscillator demonstrates, there-, fore, the independence of frequency and operating voltages. The conditions necessary for securing unity coupling will now be considered. Thefirst thing to notice, however,.in this connection is that our theory does not require that the'unity coupling condition, c

V M 'JL1LgI I should be obtained,- where L and L represent inductan-ces corresponding to reactancesi X and X respectively, What actually is required is the much less rigid condition:

Thus, imagine one 'of'the impedances, say X to consist of a 0011, L in series with a condenser,"C ,as shown in Fig. 2. We have This last expression is next separated into its real and imaginary components. Assuming, as in my copending application mentioned above, that the losses in the external circuit elements are small compared with those occasioned by the grid resistanceof then, by (7) V V p 1 2M wL L or; writing 1 r where'k may now be lessthan one, we have togetherwith C and equal to from (8) o (9) which gives the value of C necessary to provide unity coupling betweenthe plate and grid circuits at the operating frequency. Condenser C is shown connected between L 10 and L but this is not necessary. The result will be accomplished if C5 be positioned at the other side of L 1 I The value of In, practice, X X and X would usually be capacities, such as the elements C C and C respectively, in Fig. 2. 'With this arrangement, and the relation given by (10) we have the frequency from (5) The value of C is thus. written from (9) and (11) as follows:

in Equation (12) and another being that a more readily interpreted picture of the relation required for stability, namely the unity coupling condition of Equation (7 ),is ob tained.

Equation (12) is also applicable to the tuned plate-tuned grid type of oscillator, when there is magnetic coupling between the input and output circuits. Thus, when L and L are equal, as also are C and C we have from (12) (1 +k Hence, if tuning is done by ganging C and C together and varying them simultaneously, the "stability may be maintained for all frequencies by making C to consist of two parts the one a fixed capacity equal to i and the other avariable capacity ganged In order to insure fulfillment of the requirements of'this theory the oscillator should be relatively free from harmonics, in order that 7",, and r may be taken as pure resistances. v Referring to the drawingsit will be seen that the feed-back type of oscillator illustrated in Fig. 3 is obtained from the general circuit of Fig. 2 by regarding C and C as zero. Substituting zero for C and C in Equation (12) the value of G in the feedback oscillator of Fig. 3 will be When 0 and C in Fig. 2 are zero the'Hart ley oscillator shown in Fig. 4 results. The value of C in the Hartley oscillator of Fi 4. obtained by substituting zero for C and 5,, in Equation (12) will be 7 g c g a 2 0 1 l +k i v 02 i 5 r (1 k Q I If (1; and C5 in Fig. 2 are small enough to be neglected the equivalent'circuit of the reversed feed-back oscillator with grid stabili- 7 zation disclosed in my copending application mentioned above is obtained, the value of C in such an oscillatoras derived from Equation (12), or as derived in the sa-id copends ing application, being orv anode stabilization and corresponds to Fig. 2 which illustrates the general circuit for grid or control electrode stabilization.

The equation giving the 'value-of :C in

terms of the other circuit constants is obtained 7 in the manner Equation (12) was obtained and this value is f The circuits shown in Figs. 6 and 7 may derived from the general circuit shown in Fig. 5 in the same manner in which Figs. 3 and 4 were derived from Fig. 2.

In Fig. 6 a feed-back oscillator, having plate stabilization isillustrated, C and G being re arded as zero. Substituting zero for C and 5 in Equation (17 the value of (Lie 01: 1 7 In Fig. 7 a Hartley oscillator having plate stabilization is illustrated, C and 6., being made equal to zero. The value of C obtained from Equation (17) for this oscillator It 7 r 0.=%j We).

A combination of the features of'Figs. 2 and 5 may be employed in the manner shown in Fig. 8 where condensers C and C are placed in series with L and L respectively. In this case the equation for the required size of C and G becomes quite cumbersome when expressed only in terms of the other circuit constants. Since, however, the frequency is usuallyknown approximately, we may use the relation r for finding C and Cain terms of w and get:

As in the case of Figs..2 and 5, so also may the circuit of Fig. 8' be modified-to correspend to the reversed feed-back, the feedback and the Hartley types of oscillators,

stabilization being achieved both in the plate and grid circuits.

These circuits are illustrated in Figs. 9,

C and l0 and 11, respectively. In Fig. 9, C5 are regarded as zero; in Fig. 10, C and U are regarded as zero; and in Fig. 11, C3 and (hare regarded as zero. I

Since, as shown above, the frequency of an oscillator may be rendered constant independently of the tube parameters 73, and T in accordance with this invention, 'it' is evident thatexternal resistances connected between the anode and cathode and between the control electrode and the cathode, may be regarded as forming a part of 1 and 73,, respectively. Consequently, variable resistance loads may be connected in these posi tions without affecting the frequency stabilization.

Figs. 'lto 11 represent, of course, schematic circuit arrangements. Fig. 12 illus:

one of several that maybe employed and of i .VVhat is claimed is:

trates a complete oscillator wiring diagram in which the invention is employed, the oscillator being schematically shownin Fig. 11.

This wiring arrangement is, ,of course, only course similar arrangements maybe applied to the other schematic-circuits shown onthe drawings.

In Fig. 12 referencenumeral 1 designates.

a space discharge device having a cathode 2,

,an anode 3, and a controlelectrode 4:. The

cathode is energized by means of battery 5 and a positive" potential is impressed upon the anode bymeansjof battery 6. Reference numeral 7 represents a radio frequency choke coil which functions to prevent radio frequency current from flowing through battery 6. Numeral 8 designates a'by-pass condenser connected across battery 6.: A high resistance 9 of the order of 8000' ohms is'c'on- I nected across the input circuit for the purpose of perm ttingv electrons to escape from the cathode. As inthe schematic figures on the drawings L and L designate transformer windings magnetically coupled, and

included in the output and input circuits,

respectively. C is an inter-electrode condenser and G and C designate, respectively the plate and grid stabilizing reactances. Theoperation of the oscillator, is, ofcourse, obvious and well known and will not be described here. The values of C and G may I be determined from Equation (21).

Although the invention has been described in connection with certain specific embodiments it should be understood that it is not to be limited tothese embodiments and that the invention may be applied to other type oscillators includingpushrpull oscillators. Moreover, the stabilizing means may be ,anyfsuit able type of impedance and it may be asso-- ciated withthe coupling means in various ways for the purpose of accomplishing effective unity coupling without exceeding the scope of the invention.

1. An oscillator comprising an electric discharge device, input and output circuits therefor, a transformer having a plurality of windings for inductively coupling said circuits, and reactive means connectedto at least one winding of said transformer for rendering the effecti'vecoefficient of coupling substantially equal to unity.

2. An oscillator comprising a space discharge device having a cathode, anode and impedance control electrode, input and output circuits therefor, an inductance included in each of said circuits, said inductances being coupled, and a reacta'nce connected to at least one of the said inductances, the value of the reactan'ce being such as to cancel the leakage reactance between said inductances whereby the coefficient of" coupling between said circuits is equal to unity, substantially.

3. An oscillator comprising an electric discharge device having a cathode, anode and impedance control electrode, input and out-' put circuits therefor, a frequency determin 5 ing circuit energetically related to said input and output circuits, and a frequency stabilizing reactance included in said frequency determining circuit. r

4. An oscillator comprising an electric discharge device having a cathode, anode and impedance control electrode, input and output circuits therefor, a frequency determining circuit energetically related to said input and output circuits, and a frequency stabilizing reactance included in said frequency determining circuit between the control electrode and cathode.

5. An oscillator comprising an electric discharge device having a cathode, anode and impedance control electrode, input and output circuits therefor, a frequency determining circuit energetically related to said input and output circuits, and a frequency stabilizing reactance included in said frequencydetermining circuit between said anode and cathode.

6. An oscillator comprising an electric discharge device having a cathode, anode and impedance control electrode, input and output circuits therefor, a frequency determining circuit energetically related to said input and output circuits, a plurality of frequency stabilizing reactances included in said frequency determining circuit, one reactance being positioned between the anode and cathode and another reactance being positioned be tween the control electrode and cathode.

7 An oscillator comprising a space dis charge device having output and input circuits, an anti-resonant circuit included in said input circuit, means to transfer energy from said output circuit to said input circuit, and frequency stabilizing means comprising a reactance included in said anti-resonant circuit.

8. An oscillator comprising a. space discharge device having input and output circuits each including an anti-resonant circuit, a frequency stabilizing reactance included in the input anti-resonant circuit.

9. An oscillator comprising a space discharge device having a cathode, anode and control electrode, an anti-resonant circuit included between said anode and cathode,-an anti-resonant circuit included between said control electrode and cathode, a frequency stabilizing reactance included in the last men tioned anti-resonant circuit, and a reactance included between said anode and control electrode.

10. An oscillator comprising a space dis charge device having output and input circuits, an anti-resonant circuit included in said output circuit, means to transfer energy from said output circuit to said input circuit, and

control electrode, an anti-resonant circuit included between said anodeand cathode, an anti-resonant circuit included between said control electrode and cathode, a frequency stabilizing reactance included in the first mentioned anti-resonant circuit," and a reactance I includedbetween said anode and control electrode.

13." An oscillator comprising a space discharge device having output and input circuits, an anti-resonant circuit included in said output circuit, meansto transfer energy from said output circuit to said input circuit, a plurality of frequency stabilizing means eachicomp'rising a reactance, one of the said stabilizing means being included in the anti-resonant circuit andanother of the stabilizing means being included in the input circuit. r

14 An oscillator comprising a space 'discharge device having output and input circults, an anti-resonant circuit included in said input circuit, means to transfer energy from said output circuit to said input circuit, a plurality of frequency stabilizing means each comprisin'ga reactance, one of the stabil zing loo means included in said anti-resonant circuit and another of the stabilizing means included in the output circuit.. 15; An oscillator comprising a space discharge device having input and output circuits each including an anti-resonanticir cuit, a frequency stabilizing reactance included in the anti-resonant circuits.

16. An oscillator comprising a space discharge device having a cathode, anode and a cathode control, input and output circuits therefor, an anti-resonant circuit comprising an inductance and capacity included between said anode and control electrode, a portion of said inductance being included in the input ance being included in the output circuit, and

a frequency stabilizing reactance included in said anti-resonant circuit between said portions of the inductance.

'17. An oscillator comprising a space discharge devicehaving a cathode, anode and control electrode, input and output'circuits therefor, means to energize said cathode, a

circuit and another portion of said induct a, frequency determining circuit energetically related to said'input and output circuits, and V a frequency stabilizing reactanee included in said frequency determining circuit. 7 In witness whereof l hereunto subscribe my name this 13th day of March, 1931.

FREDERICK B; LLEW LLYN.

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